Input devices including proximity sensor devices (also commonly referred to as touchpads or touch sensor devices) are widely used in a variety of electronic systems. A proximity sensor device typically includes a sensing region, often demarked by an input surface, in which the proximity sensor device determines the presence, location, and/or motion of one or more input objects. Proximity sensor devices may be used to provide interfaces for the electronic system. For example, proximity sensor devices are often used as input devices for larger computing systems (such as opaque touchpads integrated in, or peripheral to, notebook or desktop computers). Proximity sensor devices are also often used in smaller computing systems (such as touch screens integrated in cellular phones).
Proximity sensors may operate by detecting changes in an electric field and/or capacitance in the sensing region. For example, the sensing region may include a number of conductors that can be configured to transmit and/or receive an electric signal. The signal can then be used to measure a capacitive coupling between various pairs of conductors. A “baseline” represents the expected capacitance for a pair of conductors when no external objects are present in the sensing region. Objects in contact with (or close proximity to) the sensing region may alter the effective capacitance of the conductors (e.g., from the baseline). Thus, a detected change in capacitance across one or more pairs of conductors may signal the presence and/or position of an object in the sensing region.